1. Field of the Invention
The present invention relates to layered manufacturing methods of fabricating earth-boring drill bits and other articles of manufacture. Particularly, the present invention relates to the use of deformable, resilient, layer-manufactured models in the production of molds for earth-boring drill bits and other articles of manufacture. More specifically, the present invention relates to deformable, layer-manufactured models that may be employed in the production of a plurality of molds.
2. Background of Related Art
Conventionally, the bit bodies of metal particulate-based earth-boring drill bits, such as tungsten carbide bits, have been fabricated in graphite molds. The cavities of graphite molds are typically machined with a five- or seven-axis machine tool. Fine features are then added to the cavity of a graphite mold by hand-held machine tools. Additional clay work may also be required to obtain the desired configuration of some features of the bit body. Thus, the fabrication of such graphite molds is typically very time consuming and expensive. Moreover, the use of graphite molds is somewhat undesirable from an environmental and health standpoint, as the machining of such molds typically generates large amounts of graphite or carbon dust.
In fabricating tungsten carbide-based or other metal particulate-based articles of manufacture, such as a bit body of an earth-boring drill bit, the cavity of the graphite mold is filled with a matrix material, such as tungsten carbide. Typically, the matrix material is then vibrated or otherwise packed to decrease the amount of space between adjacent particles of the matrix material. Next, the matrix material is infiltrated in a furnace with a molten binder material, such as a copper-nickel alloy. After the bit has cooled, the graphite mold is then typically destroyed to facilitate removal of the infiltrated bit body therefrom. Thus, the use of graphite molds may be further undesirable in that only a single bit body may be fabricated from each mold and, thus, a new graphite mold must be machined for each new earth-boring drill bit.
Direct layered manufacturing processes eliminate the need for graphite molds. Direct layered manufacturing processes have been employed to fabricate earth-boring drill bits, molds for earth-boring drill bits, and other articles of manufacture. U.S. Pat. No. 5,544,550, which issued to Redd H. Smith on Aug. 13, 1996, and U.S. Pat. No. 5,433,280, which issued to Redd H. Smith on Jul. 18, 1995, disclose the use of layered manufacturing methods to produce earth-boring drill bits and other articles of manufacture.
The direct layered manufacturing of earth-boring drill bits or other articles of manufacture includes generating a three-dimensional computer model of the drill bit or article of manufacture, creating "slices" of the computer model, and using the computer model in conjunction with layered manufacturing equipment to fabricate the article of manufacture
In operation, the layered manufacturing equipment sinters or otherwise secures a first layer of particles of a matrix material together, disposes a second layer of particles over the first layer, sinters particles in selected regions of the second layer together and to the first layer, and repeats this process to fabricate subsequent layers until the desired part has been formed from the matrix material particles.
State of the art layered manufacturing equipment and techniques have good resolution and may, therefore, be employed to manufacture parts that represent their three-dimensional computer model. Thus, once a drill bit or other article of manufacture has been fabricated from the matrix material, the particulate-based part may be infiltrated with a binder material that binds adjacent particles of matrix material together, and forms a substantially integral part that represents the computer model.
This type of layered manufacturing process is, however, somewhat undesirable since it takes a substantial amount of time (i.e., at least the length of the layered manufacturing process) to produce each layer-manufactured particulate-based part. Moreover, layered manufacturing machines that are capable of directly producing a metal part are typically expensive. Thus, the number of parts that may be produced over a given amount of time is limited by the number of available layered manufacturing machines.
Prior to infiltration, the particles of the matrices of particulate-based articles of manufacture produced by such direct layered manufacturing processes may be held together with a binder material, such as a thermoplastic polymer (e.g., polystyrene), a resin, or a low melting point metal (e.g., Wood's metal or a lead-based alloy). In layered manufacturing, the particles of metal matrix material are not, however, typically compacted to full density. The presence of binder material between particles of metal matrix material, or as a coating thereon, also reduces the density of the matrix. Moreover, due to the coefficients of thermal expansion of binder materials, and because of the space that exists between metal matrix particles and particles of binder material prior to melting or softening of the binder material, the dimensions of each layer may change during and after the layered manufacturing process, and shrink as the binder material cools. Further, prior to or during the subsequent infiltration of the matrix, thermoplastic polymer and resin binder materials are "burned out" of the matrix, exposing voids therein. Thus, direct layer-manufactured articles are typically not fully dense, and may shrink or become somewhat dimensionally distorted relative to the computer model employed to generate such articles.
In an effort to employ layered manufacturing processes to produce fully dense parts, so-called investment casting or "lost wax" processes have been employed to create a model that is subsequently used to produce a cast mold. Known layered manufacturing processes include the fabrication of plastic, wax, or paper models. Once the model has been employed to produce a mold, the model is destroyed by known investment casting processes (e.g., melting the plastic or wax or burning the paper), thereby exposing the cavity of the mold. The mold may then be employed in known processes, such as casting or forming a particulate-based matrix and infiltrating same, to fabricate a fully dense article of manufacture. After some articles of manufacture, such as earth-boring drill bits, have been fabricated in such a mold, the mold must be destroyed to remove the part therefrom. One such technique of layered manufacturing investment casting models, which may be used to fabricate earth-boring drill bits, is disclosed in British patent application serial no. 2 296 673 of Camco Drilling Group Limited (hereinafter "the British '673 Application"), which was published Oct. 7, 1996. Such investment casting processes, which employ layer-manufactured models, are, however, somewhat undesirable since the model may be employed to fabricate only a single mold. Thus, it may take longer to fabricate an article of manufacture when layered manufacturing techniques are employed to fabricate an investment casting model than when direct layered manufacturing techniques are used to fabricate the same article of manufacture. Moreover, each layer-manufactured investment casting model may be used to fabricate only one mold and, therefore, only one drill bit or other article of manufacture.
The British '673 Application also discloses the use of a layer-manufactured model that includes several pieces that are assembled prior to casting a mold and individually removed from the mold after casting. The model must then be reassembled prior to the production of another mold. As the use of a model with several individual pieces may require as many separate fabrication steps, as well as the assembly and disassembly of the pieces each time a mold is produced, that process is also time-consuming and, therefore, somewhat undesirable.
The British '673 Application discloses another method of producing molds for earth-boring drill bits, which includes employing layered manufacturing processes to produce a first mold, using the first mold to cast a deformable model, and employing the model to cast manufacturing molds. Although the deformable model may be employed to cast more than one manufacturing mold, this process is somewhat undesirable in that it requires several steps, including a layered manufacturing step, a model casting step, and a manufacturing mold casting step, to produce a manufacturing mold.
Pliable, resilient male mold models have also been cast in the cavities of machined graphite molds, then employed to form the cavities of female ceramic molds by casting the ceramic molds around the male mold model. Since the male mold model is made of a pliable, resilient material, the model may be removed from the cavity of the ceramic mold and reused to cast another female mold. This process is, however, somewhat undesirable since it requires the machining of a graphite mold. Moreover, in order to change any of the features of the mold, as is typically required by customers ordering earth-boring drill bits, a new graphite mold would have to be machined and male mold models cast therein.
Thus, a process is needed that employs a single layer-manufactured model to efficiently produce a plurality of earth-boring drill bit molds.